Work has continued on the isolation and characteristics of abnormal iodoproteins present in the soluble fraction of a transplantable rat thyroid tumor (Wollman Line 1-8R). Since these proteins react with antiserum against normal thyroglobulin (tg), they appear to be abnormal thyroglobulins synthesized by the tumor. Affinity chromatography employing anti-Tg immunoglobulin fixed to agarose (see last year's report), as well as conventional separation method, were used to partially purify two components. The major fraction ("Peak A") was excluded from gels of high pore size; and had a low sedimentation rate (approximately 8S), but did not contain aggregates. Equilibrium sedimentation in CsC1 gradients showed it to have an unusually high density (approximately 1.4). Since treatment with crude glycosidase lowered the density to approximately 1.3, this protein appears to have a very high content of carbohydrate. A second fraction ("Peak B") was retarded by gel filtration and therefore was a more symmetrical molecule; it also had a more "normal" density of approximately 1.3. Since neither protein contained thyroxine or triiodothyronine after prolonged in vivo labeling with 125I, it is possible that their abnormal structure prevented iodotyrosine coupling.